1. Field of the Invention
The present invention relates to a detection circuit, and particularly, it relates to a detection circuit for detecting a predetermined signal from a composite signal of two signals such as an oscillation gyroscope.
2. Description of the Prior Art
In a conventional gyroscope as the background of the present invention, for example, an oscillator in which a piezoelectric element is formed respectively on three side faces of a triangular prism-shaped oscillating body is used.
In the oscillation gyroscope, two out of these piezoelectric elements are used for detection, and these two piezoelectric elements or the other one piezoelectric element are used for driving.
In this oscillation gyroscope, when the driving signal is applied to the driving piezoelectric element, the oscillating body starts to oscillate. When the oscillator is rotated in this state, an output difference is produced between the two piezoelectric elements for detection, thereby the rotational anglar velocity can be known.
In this oscillation gyroscope, however, due to the processing distortion and stress of the oscillator, variations and accuracy of processing and assembling of the piezoelectric elements and the difference in their thermal expansion coefficients, temperature change and aging occur, thereby an drift component is contained in the output difference between the two piezoelectric elements for detection.
In order to prevent malfunction by the drift component, though a threshold level of an amplifier is set suitably so as not to output the input signal of the drift component level, or a DC surbo circuit is provided, or a high pass filter is disposed to change the circuit time constant, by these means, the change of output difference by the drift component and the change of output difference due to the fine rotational angular velocity can not be distinguished, and their minimum resolving power is poor and the time constant remains, thus the problem occurs in the linearity of output difference against the response speed and the rotational angular velocity.